1. Field of the Invention
The invention relates to a waste melting furnace which melts wastes of various kinds to reduce their volume, and also to a method of melting wastes by using the melting furnace.
2. Description of the Prior Art
A furnace body is composed of a furnace bottom for receiving melts, a furnace side for surrounding melts placed on the furnace bottom and the side peripheral of the space above the melts, and a furnace roof for closing the top of the space. In each of the furnace bottom, the furnace side, and the furnace roof, the inner face of a shell is covered by a thick lining for protecting the shell. A waste inlet and a gas outlet are formed in the furnace roof, a melt outlet is formed in the furnace side, and heating means for heating wastes is disposed in the furnace body (for example, see Japanese Patent Publication (Kokai tokkyo koho 6-82028).
In such a waste melting furnace, wastes charged through the waste inlet are heated by the heating means and melted so that the volume of the wastes is largely reduced. The lining for protecting the shell from corrosive gasses produced from melting wastes has a large thickness. Even when the lining is gradually eroded as a result of a long-term operation, therefore, the protection effect can still be maintained, thereby presenting a feature that the furnace can be operated continuously in a long term.
In the prior art waste melting furnace, the large thickness of the lining produces various problems as discussed below. In the furnace roof, for example, the weight is increased so that the support structure must have a high strength, and the roof has a large thickness so that the height of the furnace is large as compared with the capacity of the furnace. It may be contemplated that the furnace roof is provided with a water jacket so as to reduce the thickness of the roof. However, such a configuration is not employed because there is a danger that, when the water Jacket is broken, a large amount of water drops into the furnace to cause an explosion accident.
In the furnace side, since the thick lining is used as described above, the thickness is large. This produces a problem in that the diameter of the furnace is large as compared with the capacity of the furnace, resulting in a large installation area.
In the furnace bottom, the thick lining causes the furnace bottom to be thickened, thereby producing a problem in that the furnace is tall as compared with the capacity of the furnace. Wastes contain a large amount of heavy metals such as copper, lead, and zinc, and such heavy metals melt into a base metal in the furnace. Since such metals have a low melting point, molten heavy metals penetrate into joints and cracks of the lining of the furnace bottom, to reach the lower portion of the furnace bottom. The difference in coefficient of thermal expansion between the metals and the lining causes a problem in that the lining is damaged and the shell is melted away to cause an accident that the melts downward leak out through the furnace bottom. The leakage produces another problem in that the environment may be polluted.
In such a waste melting furnace, furthermore, the furnace roof is provided with many attachments such as the waste inlet, the gas outlet, a temperature measurement hole, and a sampling hole, and also with various parts associated with these attachments. These components must be inspected and operated in various manners. During the operation of the furnace, moreover, the upper face of the furnace roof is at a very high temperature of, for example, about 200.degree. C. This produces a further problem in that works of inspection or operation entail dangers and therefore are difficult to perform.